The idea of database saving

The idea of database keeping record
Now the site has an activity information, each activity can have a lot of users to participate, now there are two ways to save the ID of the participating users,
One is to open a field in each activity, and then the participant's ID is saved in this way (1,2,3,4), which makes it more troublesome to find the activity that it participates in according to the user (I developed with TP)
Another is to create a new database, add two fields Activeid (save the Activity ID), Joinid (Save the participant's ID), one save the activity ID, another field to save the participant's ID, as follows
Activeid joinId
1 1
1 2
1 3
This approach may result in more than one record,

------to solve the idea----------------------
The first is the normal way of NoSQL.
The second is the normal practice of SQL

If you use scenario one in a relational database (SQL), there is currently only MySQL support (found through the Find_in_set function)
But pay attention to the capacity of the field

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